1. Field of the Invention
The present invention relates to a highly-foamed-polyolefin-insulated wire having a thin insulation thickness used for data transmission in electronic devices and communication cables.
2. Description of the Background
High-speed data transmission requires electric wires used in electronic devices and communication cables to have an insulation layer with a low equivalent dielectric constant, namely, lower than 1.45. To fulfill the requirement of a low equivalent dielectric constant, an insulation layer is usually foamed by using a composite of a chemical foaming agent and polyolefin or using an inert gas. In an insulation layer made of the same material there is a correlation between its foaming degree and equivalent dielectric constant, such that the latter can be reduced by increasing the former. However, if the insulation layer of a wire is merely increased in its foaming degree, it becomes soft and susceptible to dimensional change when it undergoes a sidewall pressure at the time of or after laying of the wire. This will cause a change in electrical characteristics, reducing reliability. In particular, the recent strong demand for miniaturization of devices has compelled dense wiring, causing it to become a critical focus. The stable production of a highly foamed insulation layer with a thinner thickness is also required.